Its a electric solenoid valve, allows me to turn the water on and off using a timer l. A similar one can be found here http://autotopoff.com/Solenoids/solenoid_PP_1-4_fittings.jpg
Thanks! Interior dimensions are 7x3x3 it operates at around 400 gallons. When power is cut it fills to capacity of around 470 gal.Wow nice set up! I'm surprised how clean the tank is. Sorry if I missed it how big is that sump?